Life on Earth Is Older Than Rocks on Earth, Study Finds

Scientists believe Earth is roughly 4.5 billion years old. The oldest rocks scientists have ever found are roughly 4 billion years old. And now, a team at UCLA says it has found evidence of life that is older than those rocks.

The team, led by Elizabeth Bell, says it found "potentially biogenic carbon" in a 4.1 billion year old graphite sample that was encased in zircon, a type of crystal that is often among the oldest samples of material on Earth.

The discovery pushes back the date of the earliest evidence of life on Earth by about 300 million years, Bell wrote in a study published Monday in Proceedings of the National Academy of Sciences.

The carbon, found in the Jack Hills of Western Australia, has an isotopic ratio that has been well established to be associated with organic matter. Bell told Science that, if the sample was more recent, there would be no disputing that it was associated with bacterial life: "On Earth today, if you were looking at this carbon, you would say it was biogenic," she said. "Of course, that's more controversial [for something so old]."

Bell's paper strongly argues that the sample has biological origins and that is has not been contaminated: "Its complete encasement in crack-free, undisturbed zircon demonstrates that it is not contamination from more recent geologic processes," she wrote. She does admit, however, that the finding isn't enough to glean too much about early Earth environments during the Hadean time period (from the beginning of Earth to about 4 billion years ago) or about how life initially began. Additional findings could establish a carbon cycle (and thus an ecosystem), which would be a potentially huge finding.

"There are considerable limitations of basing any inference regarding early Earth on a single zircon," she wrote. "Confirming [this finding with additional discoveries] would represent a potentially transformational scientific advance. However, given the low occurrence of carbon-bearing Hadean zircons, establishing a Hadean carbon cycle and its possible bearing on the origin of life will require enormous and sustained efforts."